There has been a rapid rise in the prevalence of allergic diseases over the last several decades in industrialized countries, especially in young children. The hygiene hypothesis proposes that normal immune maturation and resistance against allergy is in part a consequence of immune provocation from microbial flora and infections. It is well accepted that allergic diseases also have a strong genetic component. This genetic component may influence the host's response to environmental agents that modulate the development of allergic phenotype. The family of the toll like receptors (TLRs) and its related signaling molecules offers a conceptual and practical framework within which the hygiene hypothesis can be examined. Thus, the first project will probe the repertoire of genes that link environmental immunostimulants (i.e., microbial TLR ligands) and allergic asthma utilizing a mutagenesis approach to identify genes that block the ability of certain microbial TLR ligands to prevent allergic inflammation. Mutations will be isolated through positional cloning. The genes involved will be well characterized and the human orthologs of these genes will be analyzed by DNA sequencing in asthma patients. The second Project will study the impact of environmental (microbial) factors on the development of the allergic phenotype in a molecularly defined model of TLR ligand deficiency using a variety of related knockout mice. The third Project will attempt to identify the biochemical and molecular pathways that collaborate to inhibit allergic inflammation at the level of innate immunity, while the fourth Project will address the contribution of TLR ligand activated adaptive immunity to the inhibition of the allergic phenotype. Each of the four cores will support different aspects of these synergistic and interactive projects. Administrative Core, will facilitate the collaborations and the interweaving among the projects. The Animal Core, will provide the necessary knockout mice for genetic and immune dissection. TLR Ligand Core, will generate and quality-control microbial reagents, Assay/Procedure Core will provide laboratory services.